Restriction endonuclease analysis of genomic DNA from 24 inbred and 8 wild mouse strains have been carried out using the Southern blotting technique and a xenotropic reactive recombinant DNA probe. Except for 3 distantly related mus species the DAN from all mice tested contained numerous (18-28) xenotropic reactive HindIII fragments. Of these 4 were found common to all inbred and most wild mice tested. Because many common "bands" were found in closely related mice with fewer compating "bands" in more distantly related strains we were able to use these patterns to measure genetic relatedness between the various strains and to demonstrate an AKR genetic contamination of the high leukemic C3H/Fg strain. Such contamination is not found in the low leukemic C3H parent. Our studies of the internal organization of the various xenotropic related proviral sequences have allowed us to define at why some of these endogenous sequences are expressed as xenotropic virus, as MCF recombinant type virus or not at all in some mouse strains but not others, continues as the primary long range goal of this project.